tmpfs: distribute interleave better across nodes

When tmpfs has the interleave memory policy, it always starts allocating
for each file from node 0 at offset 0.  When there are many small files,
the lower nodes fill up disproportionately.

This patch spreads out node usage by starting files at nodes other than 0,
by using the inode number to bias the starting node for interleave.

Signed-off-by: Nathan Zimmer <[email protected]>
Signed-off-by: Hugh Dickins <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Lee Schermerhorn <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Andi Kleen <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/shmem.c

@@ -929,7 +929,8 @@ static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
 
 	/* Create a pseudo vma that just contains the policy */
 	pvma.vm_start = 0;
-	pvma.vm_pgoff = index;
+	/* Bias interleave by inode number to distribute better across nodes */
+	pvma.vm_pgoff = index + info->vfs_inode.i_ino;
 	pvma.vm_ops = NULL;
 	pvma.vm_policy = spol;
 	return swapin_readahead(swap, gfp, &pvma, 0);
@@ -942,7 +943,8 @@ static struct page *shmem_alloc_page(gfp_t gfp,
 
 	/* Create a pseudo vma that just contains the policy */
 	pvma.vm_start = 0;
-	pvma.vm_pgoff = index;
+	/* Bias interleave by inode number to distribute better across nodes */
+	pvma.vm_pgoff = index + info->vfs_inode.i_ino;
 	pvma.vm_ops = NULL;
 	pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, index);